This invention relates to a process for mounting a semiconductor device on a wiring board. More particularly, it relates to a process for mounting a semiconductor device whereby a bare chip is directly mounted on a substrate by using an anisotropic conductive adhesive film.
To mount a bare chip directly on a wiring board such as a print wiring board, there has been known a process with the use of an anisotropic conductive adhesive film having conductive particles dispersed in a binder.
In this process for mounting a bare chip on a wiring board by using an anisotropic conductive adhesive film, it has been a practice to form protruding bump electrodes in the IC chip side or in the wiring board side.
This is because, in case of bumpless connection without forming any bump, conductive particles sometimes come into contact with the scribe line at the edge of the IC chip thereby causing a short-circuit.
In recent years, there has been required fine pitching between the electrodes of a wiring board of the above type. To satisfy this requirement for fine pitching, the connection electrode area between the wiring board and the IC chip should be reduced.
To achieve fine pitching in practice in the conventional mounting process, it is necessary to surely provide conductive particles between the electrodes. To ensure the existence of the conductive particles, it is suggested, for example, that the conductive particle diameter is further reduced so that a larger number of conductive particles can be contained in the binder of the anisotropic conductive adhesive film.
However, an increase in the content of the conductive particles in the binder is accompanied by an increase in the viscosity of the anisotropic conductive adhesive film and, in its turn, a decrease in the fluidity of the conductive particles in the binder. As a result, it becomes difficult to uniformly disperse the conductive particles in the binder. At the same time, there arises another problem that the insulation properties of the anisotropic conductive adhesive film are deteriorated.
When the conductive particle diameter is reduced, on the other hand, the absolute deformation caused by crushed conductive particles in the step of the thermocompression bonding becomes smaller and thus the irregularity in the bump electrode height cannot be compensated thereby. In such a case, it is feared that some of the electrodes of the wiring board and the IC chip undergo connection failure and thus the conduction reliability is lowered.
As discussed above, fine pitching cannot be sufficiently established in practice in the conventional mounting processes.
An object of the present invention, which has been completed to solve these problems encountering in the conventional art, is to provide a process for mounting a semiconductor device whereby electrodes of a fine-pitch semiconductor device and a wiring board can be surely connected to each other.
Another object of the present invention is to provide a process for mounting a semiconductor device whereby the occurrence of a short-circuit between a semiconductor device and a wiring board can be prevented in a bumpless IC chip.
According to the present invention, which has been made to achieve the above-mentioned objects, it is provided a process for mounting a semiconductor device by electrically connecting electrodes of the semiconductor device to electrodes of a wiring board, which process comprising; the step of tentatively thermocompression bonding a conductive particle-free filmy insulating adhesive to the wiring board and then forming an insulating adhesive layer having a concave of a predetermined size in the insulating adhesive layer; and the step of putting the anisotropic conductive adhesive film having conductive particles dispersed in an insulating adhesive, in the concave of the insulating adhesive layer and then putting the semiconductor device in the concave followed by positioning and thermocompression bonding.
In thermocompression bonding with the use of an anisotropic conductive adhesive film, it is generally observed that conductive particles tend to run off together with the insulating adhesive toward the edge of the IC chip. In the case of the present invention, however, the conductive particles tending to run off toward the IC chip edge are blocked by the brim of the concave formed in the insulating adhesive layer. Thus, the conductive particles scarcely f low in the direction of the IC chip edge.
According to the present invention, therefore, the conductive particles can be densely held between the semiconductor device and the wiring board. Thus, plural conductive particles can be provided on each electrode at an extremely high probability and connection electrodes can be surely electrically connected to each other without fail even in a case where connection electrodes are located at very small intervals.
According to the present invention, moreover, no conductive particle reach the scribe line part of the IC chip edge and, therefore, there arises no short-circuit between the scribe line and the wiring board.
According to the present invention, a fine-pitch semiconductor device can be surely mounted on a wiring board with the use of only a small amount of conductive particles as described above, which contributes to the cost reduction.
In the present invention, it is also effective that the inner wall of the concave of the insulating adhesive layer is located inside the scribe line of the wiring board but outside the outmost edge of the connection electrode of the semiconductor device.
According to the present invention, conductive particles in a larger amount can be provided on each connection electrode and the occurrence of a short-circuit between the scribe line and the wiring board can be surely prevented.
According to the invention, it is also effective that the concave of the insulating adhesive layer is formed in such a manner that it has a depth less than the thickness of the bare chip but more than the size (nearly equal to outer diameter) of the conductive particles in the anisotropic conductive adhesive film.
According to the present invention, run of f of the conductive particles can be more effectively prevented in the step of the thermocompression bonding and a thermocompression bonding head can be prevented from stains caused by the insulating adhesive resin squeezed out from the IC chip.
According to the present invention, when the insulating adhesive layer has a melt viscosity larger than the melt viscosity of the anisotropic conductive adhesive film, then the run off of the conductive particles can be surely prevented. Thus, the occurrence of a short-circuit between the scribe line and the wiring board can be prevented without fail and, at the same time, the existence of a larger number of conductive particles can be ensured on each connection electrode.
It is particularly advantageous in lessening the run off of the conductive particles that the melt viscosity of the insulating adhesive layer is from 1xc3x97106 to 1xc3x97109 mPaxc2x7s.
According to the present invention, it is effective to use as the anisotropic conductive adhesive film containing conductive particles surface-coated with a resin having a softening point higher than the temperature at which the insulating adhesive layer is tentatively thermocompression bonded.
According to the present invention, the conductive particles are surface-coated with an insulating layer and, therefore, the conductive particles can be employed in a larger amount. Thus, the number of the conductive particles existing on each connection electrode can be increased and the conduction reliability can be elevated.
In addition, it is also effective in the present invention that using the anisotropic conductive adhesive film having an average particle diameter of the conductive particles of from 1 to 10 xcexcm and a content of the conductive particles of from 1 to 15% by volume.
According to the present invention, the conduction resistance can be reduced and the conduction reliability can e elevated. In this case, moreover, the insulation resistance between electrodes adjacent to each other can be increased.
On the other hand, it is also effective that the following relationship is satisfied in the process:
v1+V2xe2x89xa7V3+V4
wherein V1 stands for the volume of the insulating adhesive layer; V2 stands for the volume of the anisotropic conductive adhesive film; V3 stands for the volume of the adhesion part of the wiring board; and V4 stands for the volume of the contact hole in the pad of the bumpless semiconductor device, as in the present invention.
According to the present invention, a fine-pitch semiconductor device can be surely mounted on a wiring board without forming any bump.